Lateral cortical stress reactions have been documented to precede femoral insufficiency fractures after long-term bisphosphonate therapy. We studied the natural history of femoral stress lesions associated with long-term bisphosphonate therapy.

A retrospective clinical and radiologic review of all patients with radiologically documented femoral stress lesions associated with bisphosphonate therapy was carried out in a tertiary center involved with geriatric trauma care.

Of 1463 geriatric hip fractures occurring from May 1, 2004, to July 31, 2008, 33 were of a distinct metaphyseal-diaphyseal configuration. Thirty-two were on prior bisphosphonate therapy. Sixteen femurs showed a lateral cortical thickening either on prefracture radiographs (four femurs) or on radiographs of the contralateral femur (12 femurs).

Features that predispose to complete stress fractures were determined. The intact femurs were followed up for symptomatic and radiologic progression and occurrence of new lesions.

All four cases that fractured had a "dreaded black line" in the lesion, whereas only 1 of 12 patients had this fracture in femurs which remained intact (100% versus 8.3%, P = 0.003). All patients who fractured reported thigh discomfort over 1 month (range, 0.1-9.0 months; standard deviation, 4.0 months), whereas three of 12 patients who did not fracture reported thigh discomfort (100% versus 25%, P = 0.019). In the remaining patients, eight patients were asymptomatic, two patients had reduced symptoms, and one patient had persistent thigh pain at 23.0 months (range, 5-35 months; standard deviation, 10.2 months). One patient was too demented for symptomatic assessment. No patient developed a new lesion. Radiologic stabilization of the lateral cortical thickening was evident on follow-up radiographs.

Cortical stress reactions associated with prolonged antiresorptive therapy, in the presence of pain and the "dreaded black line," have an increased risk for complete stress fractures.

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